Viscose and process for making



Reissued Aug. 21, 1934 PATENT OFFICE p VISCOSE AND PROCESS FOR MAKINGSAME Leon Lilienfeld, Vienna, Austria No Drawing. Original No.1,658,607, dated February '7, 1928, Serial No. 646,240, June 18,

1923. Renewed November 23, 1927.

Application for reissue November 3, 1932, Serial No. 641,119. In AustriaMarch 15, 1923 27 Claims.

I have made the discovery that in the manufacture of viscose theapplication of temperatures below C., for example temperatures between 0and 25 C. or lower, produces surprising effects which aifordconsiderable advantages to the viscose art.

These efiects are to be seen in the following directions:

- The application of cold during the sulphidizing and dissolving stages,but particularly the latter stage makes possible the production ofviscose in one continuous operation. Thus, for example, it is possiblewithout further ado to convert cellulose mixed with dilute alkalisolution into a '15 technically valuable viscose solution by treatingwith carbon bisulphide and subsequently cooling.

By suitably conducting the process, it is even possible to combine themixing of the cellulose with the alkali solution, the sulphidizing andthe dissolving practically in one operation.

The following examples are given for this modification of the process:

(a) Mixtures of cellulose with dilute alkali solutions (for examplecaustic soda solution of from 4 to 12 per cent. strength) which evenwhen treated for many hours with small to moderate quantities of carbonbisulphide (for example to of one molecular proportion of carbonbisulphide to one molecular proportion of CsHioOs) at room temperatureare not dissolved or are only incompletely dissolved, but yield productswhich even after addition of stronger alkali solution do not dissolve'ordissolve incompletely, are converted with remarkable speed into perfectviscose solution after being subjected to the action of carbonbisulphide even for quite a short time, for instance 5 to minutes, ifthey are subjected to the influence of'low temperatures.

(1)) Mixtures of cellulose with dilute alkali solution (for examplecaustic soda solution of 48 per cent. strength) which when treated formany hours even with large proportions of carbon bisulphide (for exampleto 1 molecular proportion of carbon bisulphide to one molecularproportion of CsH10O5) at room temperature do not pass or pass onlyincompletely into viscose solutions, and yield only products whichdissolve completely only after addition of stronger alkali solution(that is after increasing the strength of the caustic soda solutionpresent, for example to 10-12 per cent), are converted withextraordinary rapidity into perfect viscose solutions even after quiteshort action of carbon bisulphide, for example for 5 to 30 minutes. ifthey are subjected to the influence of low temperatures.

(0) Mixtures of cellulose with alkali solutions (for example causticsoda solution of 9-12 per cent. strength) which at room temperature passinto complete or nearly complete solution only after several hourstreatment with large proportions of carbon bisulphide (for example l-lmolecular proportions of carbon bisulphide to one molecular proportionof CsH1uO5), are converted with great speed into perfect viscosesolutions even after quite short treatment, for example for 5 to 30minutes, with carbon bisulphide, if they are exposed to the influence oflow temperatures.

(d) Alkali-cellulose which requires several hours treatment with carbonbisulphide at room temperature before it yields a product that dissolvescompletely at normal temperature on addi tion of water or alkalisolution, dissolves in water or alkali solution even after quite shortaction (5 to 30 minutes) of the carbon bisulphide, if the solutionoccurs at a low temperature. v

In addition to the possibility of starting from cellulose mixed withalkali solution and converting it into viscose in one continuousoperation, further advantages accrue from the invention when the parentmaterial is .a true alkali cellulose, that is to say a product obtainedby mixing cellulose with alkali solution of 15 to 50 per cent. strength,or by impregnating cellulose with'such solution, removing the excess bymore or less pressure or by centrifuging or the like and, wherenecessary, disintegrating the residue.

The possibility of shortening the process and radically reducing theamount of carbon bisulphide is also of benefit to the alkali cellulose.Moreover, the tendency-enhanced or developed by the coldof thesulphidized alkali cellulose to pass into solution, permits ofcurtailing considerably the mercerizing and ripening operations, or evenof eliminating the latter altogether, and of simplifying thedisintegrating operation or of substituting for it a simple looseningoperationcircumstances which considerably reduce the deleteriousinfluence of the alkali. In addition, the application of lowtemperatures according to the invention to sulphidizing and dissolvingor to dissolving alone, makes the solutions more perfect.

I An important advantage of the inven ion consists in the possibility ofreducing the proportion of carbon bisulphide far below that hithertocustomary in viscose manufacture. For example, even about 1/40 to of amolecular proportion of carbon bisulphide per molecular proportion ofcellulose CsHicOs, that is an amount of carbon bisulphide weighing fromi to of the cellulose used, suffices to yield technically useful viscosesolutions.

When the invention is applied with the use of very small proportions ofcarbon bisulphide, there are obtained viscose solutions which even inthe crude state are practically colorless and odorless and keep forweeks. As shown even by the very small consumption of carbon bisulphide,such viscoses exhibit a novel, high molecular composition. They yieldthe characteristic reactions of viscose, such as coloration withmetallic salts, the iodine reaction, and splitting off of carbonbisulphide. They are ready for use even when freshly made, that is tosay they are capable of being spun and worked up into all the productsthat come into consideration. A further advantage is that when formedintothreads, films, plates and the like they do not become milky in theprecipitating baths. Their coagulability is considerable. Even diluteinorganic or organic acids alone, salt solutions, dilute alcoholsolutions and the like suiiice to solidify such viscoses in sheet orfilament form. Accordingly, the working up of such viscoses intotechnical products is simpleand cheap.- 7

In view of the proportions of carbon bisulphide used, such viscoses cancontain only slight proportions of carbon bisulphide residues. Assumingthe. maximum limit for the proportions of carbon bisulphide used in themanufacture of such viscoses poor in carbon bisulphide residue to be/6th molecular proportions of CS2 per 1 molecular proportion of061-11005 and the minimum to be 1/40 molecular proportion of CS2 per 1molecular proportion of CeI-IioOa, the following theoretical limitingformulas may be given for the final products of those modifications ofthe invention in which such small proportions are used:

Cm 4ooOm,O.CS.SH OsoHnOn.0.0S.SH

Minimum limit Maximum limit between which formulas every possibletransition stage must be included.

The fact that according-to the present process xanthate stages can beproduced within the limits C36 aHd'CZLO is all the more surprising asthe chemistry of viscose starts, as known from'the assumption that thestage C36, which hitherto could be obtained only by decomposition ofnormal viscoses, forms the limit and that even the xanthate C411 is notcapable of existing, because at the moment of its formation itimmediately decomposes leaving cellulose-hydrate.

xanthate C48 capable of existence, but even xanthates which contain amuch smaller proportion of carbon bisulphide residues. What is stillmore important, however, is that they show that such xanthates aresurprisingly durable and have ex- 1 viscoses having valuable technicalproperties, in

no wise detracts from its value when larger proportions of carbonbisulphide are used. Asthe latitude allowed between the maximum limitassumed above molecularproportion of CS2 to 1 molecular proportion ofC6H1005) and the proportions of carbon bisulphide usually employed inthe manufacture of viscose (about one molecule of CS: per one moleculeof cellulose CsHioOs) is very large and as, according to the invention,

' technically valuable viscoses are produced irre- 7 rate methods.

The results of thisinvention show that not only is the spective of theamount of carbon bisulphide employed, a sharp, quantitative limit cannotbe drawn. The most valuable technical efiects of the application ofcold, namely a more rapid and simpler production and a thoroughconservation of the cellulose and an improvement of the final viscosesolution are realized in every case, so that the invention is applicablewith small, medium and large proportions of carbon bisulphide.

' As parent materials for the process, owing partly to its simplicityand partly to the. admissibility of small amounts of carbon bisulphide,there come into consideration not only the parent materials commonlyused in viscose production, but also bodies which may be obtained fromcellulose by somewhat more elabo- The following are given by way ofexample: bleached or unbleached cellulose of every kind, cellulosecontaining materials, mechanically or chemically hydrated or hydrolizedcellulose (for instance by grinding it with water, or by treating itwith strong mineral acid in the warmth or with zinc halides in thepresence or absence of acid, or with copperoxide ammonia), oxycellulose,mercerized': cellulose with or without being washed and with or with-.out being treated with a dilute acid,.artificial threads produced fromconversion products or derivatives of cellulose, artificial silk-waste,etc.

In the following part of the description and in the claims, the termcellulose or parent. material, wherever the meaning permits, is in,tended to include any of the materials'enumer ated in the foregoingparagraph.

Several methods of introducing the alkali to the parent material areafforded, of which the most important three will now be recited:

Method 1. The parent material is converted into alkali cellulose inknown manner, that is the like, so that the residue contains, forexample,

1-5 parts by weight of the alkali solution to 1 part by weight ofcellulose.

Method 2.-The parent material is mixed with 1-5 times its weight ofstrong alkali solution, for example caustic soda solution of 15-50 percent. strength, by hand or, preferably, in a suitable mixing apparatus.

Throughoutthe description andclaims, whereever alkali-cellulose ismentioned, products in the sense of those obtainable according toMethods 1 .or 2 are implied.

M ethod 3.-The parent material is mixed with dilute alkali solution, forexample caustic soda solution of 3-12 per centrstrength; for example,either by mixing the parent material as such with the alkali solution orby previously producing its alkali compound (alkali-cellulose) accordingto Method 1 or 2, and then, according to the content of alkali alreadypresent, mixing either with water or alkali solution, so that the alkalimay be present in the mixture in the desired pro-' portion andconcentration. The parent material.

may be mixed with alkali solution or the alkali cellulose with water or.alkali solution manually or in a stirring, kneading'or disintegratingapparatus. The final mixture may be so constituted for this purpose (forexample caustic soda solution of :4 to per cent. strength amounting to 8to 24 times the weight of the air-dry parent material); or: it maycontainless or weaker or strongera1kali'solution.

Wherever mention is'made in the description or in the patent claims-ofmixture of cellulose with alkali solution or of cellulose being mixedwith alkali solution, there are implied mixtures in thesense of thoseobtainable according to Method 3 as described in the foregoingparagraph. v r

"The parent material chargedwith alkali according to Method 1,-2 or 3 isnow, where necessary after several hours or several days standing(ripening), treated with carbon bisulphide and dissolved. If alkalicellulose produced-according to Method 1 or 2 is subjected as such tothe action of carbon bisulphide, sulphidizing and dissolving must'occurin two separate operations, since the amount and concentration of thealkali solution are, as a rule unsuitable for the dissolution of thecellulose. If mixtures in the sense of Method 3 are used, sulphidizingand dissolving may then formone continuous operation, in certaincircumstances evenpractically speakingone procedure.

' In the treatment with carbon bisulphide and in dissolving, butparticularlyin dissolving, the basic principle of the presentinvention-the cold-is applied.

In this connection the following directions, to which, however, theinvention is not to be con.- fined, may be observed:

A. Sulphidizing and dissolving are conducted at temperatures below 0 C.,for example between 0 and C. or lower.

B. Sulphidizing is conducted partly at temperatures above 0 C., forexample between 0 and C. or higher and partly at temperatures below 0C., preferably at temperatures between 1 ties: sulphidizing is begun attemperatures above 0, for example between 0 and '+30 C. and is completedtogether with the dissolving at temperatures below 0 C., preferably attemperatures between 0 and 25 C. or lower; or sulphidizing is begun attemperatures above 0 C. for example between 0 and +30 C., or higher, iscontinued simultaneously with dissolving at temperatures below 0 C.,preferably at temperatures between 0 and 25 C. or lower and is completedat temperatures above 0, for example between 0 and +30 C. or higher.

C. Sulphidizing is conducted wholly at temperatures above 0 C., forexample between 0 and +30 C. or higher and solution at temperaturesbelow 0 C., for example at temperatures between 0 and 25 C. or lower.

Accordingly, "the practical conduct of the process may be, for'example,as follows:

In a vessel or apparatus such as is commonly used for the purpose thereis placed alkali ce1lulose (produced by treating the initial materialaccording to Method 1), with carbon bisulphide which is allowed to act,preferably while shaking or stirring; fora short or prolonged period(for example from' 5 minutes to 48 hours) either at +2'C. or lower, forinstance between 0 and 5 C., or above 0 C., for instan'ceat room tern--perature ,or higher, for example between +20 C. and +30 C. '5 Then,according to the alkali-content offthe'alkalicellulose, there is addedsomuch C. or lower, whereby the viscose solution is quick-.

1y formed.

Or, to a mixture of the parent material with alkali solution (preparedfor example as per Method 3) contained in a vessel adapted to be closed,carbon bisulphide is added and allowed to act, preferably while shaking,stirringor agitating the mixture, for a short or prolonged period (forexample from 5 minutes to 48 hours) either at +2 C. or lower, forexample between 0 and 5 C. or above 0, for example at room tem-;-*

perature. The mass is then subjected to the action of temperatures below0 C., for example of temperatures between 0and 25 C. or lower, andpreferably while stirring, whereby the viscose solution is quicklyproduced. Its viscosity may be regulated by addition of alkali solutionduring the cooling action or subsequently.

All the foregoing methods, given by way of example, of carrying out theprocess have the common feature that dissolving occurs at lowtemperatures either during or after or before the treatment of thecellulose with carbon bisulphide in presence of alkali.

It is owing to this feature that the carrying out of the process is,practically speaking, subject to no restrictions or nearly so, inrespect of temperature and duration of the action of carbon bisulphide,provided this action proceeds wholly or in part before solution, that isbefore the cooling action begins. Experience teaches that a widelatitude is allowable in this respect.

The temperature required to produce viscose solutions as perfect aspossible depends partly on the strength of the alkali solution containedin the mixture, partly on the proportion of carbon bisulphide used andpartly on the chemical and physical properties of the parent material.

As a general rule to be applied to temperature, it may be stated thatthe desired result, that is to say a perfect viscose solution, isobtained in every case at a temperature between 5 and -'-l2 C., if notat a higher. This rule applies also to cases in which even highertemperatures, for

example between 0 and 5 C. lead to-the desired end.

At temperatures below 8 to 9 C., particularly if the alkali solution isvery dilute (for example caustic soda solution of 6 per cent. strength)and vigorous stirring is applied, the reaction masses usually showcrystal formation or freeze. "With the use of stronger alkali solutions(for example caustic soda solution of 10 to 12 per cent. strength) themasses, certainly, do not freeze or crystallize quite so readily, but doso fre quentlyat -9 to 12 C. if stirring is vigorous. This phenomenon inno wise impairs the quality of the'final' product. In very many cases itis even advisable to continue the cooling action up 1 to the freezing orcrystallizing stageand to keep the mass in this state for a short orprolonged period.

The formation of the viscose solutioneffected in the coldhaving beenvcompleted, the cooling i immediately or shortly after a test portionshows that solution is complete and that asmall test film quicklyprepared (for example by spreading Y the solution on a glass plate andtreating with a suitable precipitating bath, such as sulphuric acid of-20' per cent. strength) exhibits the desired clarity: and strength.Cooling may, however, be continued. -But in many cases, for example inthose where quite small proportions of carbon bisulphide are used, it isadvisable not to prolong the period of cooling overmuch beyond the pointat which complete dissolution has occurred, because insuch cases thesolution is liable to acquire a gelatinous character or to gelatinizecompletely or to turn muddy, owing to too prolonged cooling action.

I It is advisable to stir or knead or to keep the .;i mass in movement,intermittently or continuouslyv during the cooling operation.

In the following examples the parts are by weight:

(a) 50 to 100 parts of air-dry, preferably finely crushed sulphitecellulose or bleached cotton, for example medicated cotton wool, aremixed with 900 to 1900 parts of caustic soda solution of 8 to 10 percent. strength at room temperature, preferably while stirring orkneading, until the mixture is homogeneous. The period of mixing orstirring may be only 10 to minutes, particularly when the parentmaterial readily absorbs the caustic soda solution and is rapidlysubdivided therein. The mixture may, however, be stirred for hours orallowed to stand, so

as to obtain a uniform saturation of the parent,

material with the caustic soda solution. When the mixture ishomogeneous, carbon bisulphide is added in the proportion of to parts to100 parts of parent material; the vessel is closed and the mass stirred,kneaded, shaken or otherwise kept in motion for 10 to 15 minutes at roomtemperature. The mixture is then cooledpreferably in the same vessel,which is provided with an external or internal cooling device, or both,adapted to produce low temperatures (for example a cooling bath at about16 to 25 C., into which the vessel is placed, or a cooled double jacketwith or without cooled mixing wings, or a cooling coil or the like)andduring this operation the mass is stirred, kneaded, rubbed or agitated,the vessel being open or closed. Cooling is so conducted that thetemperature of the mass cannot fall substantially below 10 to 11 C. Atabout 8 to 10 C. the mass begins to exhibit crystal formation or tofreeze slightly, which phenomenon becomes more pronounced as thetemperature continues to fall. As soon as the temperature of the mixturefalls to '10 to 11 C. it is usually frozen to a soft, lard-like mass,the consistence of which, however, permits further stirring. Afterkeeping the mass at 10 to 11- C. for 30-40'minutes,

- room temperature.

cooling is interrupted and the frozensolution thawed, preferably whilestill stirring, either at room temperature, or in order to acceleratethe operation, with the application of gentle heat.

consumed .and very finely subdivided carbon bisulphide. The milkyappearance vanishes, however, immediately, or soon after, the viscosesolution is at room temperature. There is produced a viscose solutionrelatively little colored and practically free from undissolvedconstituents, which during 14 days at room temperature shows no visiblechange, so that it may be described as stable for this period, at least.It may be Worked up, without further treatment, into technical products;spread upon a' glass plate and treated with dilute sulphuricacid (for'ex-' ample of 10-20 per cent. strength) it yields .a temporarily milkyfilm, which becomes clear after long standing in the. acid. Afterwashing and drying the film is transparent and remarkably flexible.

(b) The mode of operation is exactly as in (a), except that to 100 partsof parent material only 20 to 25 parts of carbon bisulphide are used.The coloration after treatment with carbon bi sulphide is scarcelyappreciable. After thawing, the viscose solution is'certainly milky, butnot the degree attained by that in Example .I (a). Accordingly, themilky appearance vanishes somewhat more rapidly than in that case. Thereis produced a clear, scarcely colored viscose solution, practically freefrom undissolved constituents, which, during 13 days at room temperatureshows no visible indications of a change. lf'ilms produced therefrom aretemporarily milky in the wet state, become perfectly clear after aprolonged period in the acid and are transparent and flexible in the drystate.

(c) The mode of operation is exactly as in ((2), except that to 100parts of parent material 10 to 15 parts of carbon bisulphide are used.There is no appreciable coloration after the carbon bisulphidetreatment. After thawing, the product is a scarcely colored viscosesolution which is clear from the first and contains no undissolvedconstituents. A film made from it is, from the first, clear and strongin the dilute acid and flexible after'washing and drying. During 14 daysat room.-temperature, the solution shows no signs of a change.

(d) The mode of operation is exactly as in (a), except that only5 to 6parts of carbon bisulphide are used to 100 parts of parent material.There is no appreciable coloration after the carbon bisulphidetreatment. Thefmixture is kept at l0 to 11 C. from 3 to 10 minutes only.The mass thaws to a viscose solution which is clear from the first,almost colorless and liquid and shows no visible change after 10 days atIt yields films which are transparent and flexible both in the wet andin the dry state.

'-In the foregoing examples there may be used also a weaker solution ofcaustic soda, for instance such of 6 per cent. strength. The dura-' tionof the action of carbon bisulphide may be prolonged for example up to 12hours. The time of the action of low temperatures (10to 11 C.) may beshortened to 1 to 3 minutes.

Instead of wood pulp or cotton there may be employed acellulose hydratedby mechanical 'or' physical" means for example according to thefollowing formulas:

1) 200 parts of sulphite cellulose in fleeceor sheet-form are stirredwith 10 to times their weight of water until the mixture is homogeneousand after standing for several hours or several days at room temperaturethe mixture is reduced to 250 to 350 parts by weight by pressing orcentrifuging. The compressed cake or residue is then ground or crushedfor several hours up to eight days in a suitable apparatus (for example,a disintegrator, shredder, beater, willowing machine, devil or kneadingapparatus) and optionally dried.

(2) 100 parts of sulphite cellulose in fleeceor-sheet-form or medicatedcotton wool are saturated with 900 to 1000 parts of a caustic sodasolution of 18 to percent. strength at room temperature andleft in thissolution for 6-24 hours; the whole is then reduced to 200 to 300 partsby weight by pressing or'centrifuging and comminuted or disintegrated ina suitable apparatus (for example a disintegrator, shredder, beater,willowing machine or devil). The sodacellulose, either immediately afterdisintegration or after standing for 1-3 days at room temperature, isthen stirredv with cold or hot water, washed, pressed or centrifuged anddried in a vacuum or in the air, or used in the pressed or centrifugedstate,'in which case the proportion and strength of the caustic sodasolution to be added must be adapted to the water-content. Afterwashing, the mercerized cellulose may still be treated with a diluteacid (for example sulphurlc acid of 10 per cent. strength) and againwashed, centrifuged or pressed and, if desired, dried.

(a) 100 parts of mercerized cellulose as in Example I (2), or 100 partsof medicated cotton wool, or 100 parts of sulphite cellulose or aquantity' of the parent material as described in Example I' (1).corresponding with 100 parts by weight of air-dry sulphite cellulose aremixed with 1200 to 1900 parts of caustic soda solution of 8 per cent.strength until the whole is homogeneous. g parts of carbon bisulphide,are then added, thevessel is closed brought ,to l.C. and keptat. thistemperature for "6 hours, while periodically stirring, shaking or'thelike. After this period, no solution is formed, but'a'light yellow,fibrous paste, which,

spread upon a glass plate and treated with dilute sulphuric acid. yieldsnofilm, but an opaque, decomposing residuer, The-massis then cooled to910 to 11 C. and keptat this temperature for about l-zminutes. The veryslightly crystallized or frozen mass is brought to room temperature,when it becomes a clear, fluid solution of viscose of the color of whitewine and practically free from undissolved constituents. The solutionyields'a temporarily milky film, which after a considerable period inthe acid becomes perfectly ';clear and strong and after washing anddrying istransparentand flexible. During 10 days at room temperature nochange is visible in the summon. e

- '(b) The mode of operation is as in (a), except thatonly 8 parts ofcarbon bisulphide are used that the 6-hours sulphidizing operation iseffected at 0 C. In this case also, no solution occurs and the massyields no film. The viscose solution obtained differs from that obtainedin (a) only in'being of a lighter color. In all other' andthe mixturequickly,

5 respects, the behavior of the solution and of the films is as in (a).

III

(a) 100 parts of mercerized cellulose as in Example I (2), or 100 partsof medicated cotton wool, or 100 parts of sulphite cellulose or aquantity of the parent material as described in Example I (1)corresponding with 100 parts by weight of air-dry sulphite cellulose aremixed with 1200 to 1900 parts of caustic soda solution of 10 per cent.strengthuntil the mixture is homogeneous. 40 parts of carbon bisulphideare added and the whole is treated therewith for 2 hours at roomappreciable coloration occurs. This mixture is then brought, whilestirring, to 5 C. and kept at this temperature for 5-10 minutes. Theslightly milky, complete solution becomes perfectly clear when broughtto room temperature. There is formed a fluid, clear solution of viscoseof a White wine color, practically free from undissolved constituents.The solution yields a film which turns temporarily hazy in dilutesulphuric acid, but then becomes and drying is transparent and flexible.

(b) The mode of operation is exactly as in (a) except that only 5-10parts of carbon bisulphide 100 parts of sulphite cellulose or medicatedcotton wool or a quantity of the parent material as described in ExampleI (1) corresponding with 100 parts by weight of air-dry sulphitecelluloseare mixed with 1900 to 2400 parts of caustic soda solutionof8-10 per cent. strength until the mixture-is homogeneous, 20 parts ofcarbon bisuiphideare added and the whole is stirred .or shaken or thelike for 3 hours at room tempera ture. After this period no solution isformed, but a slightly colored flbrousmixture. A part or the mass isseparated from the bulk, and kept at room temperature for 10 hours. Evenafter this period no solution is formed, but only a swollen fibrouspaste which, spread upon a glass plate and treated with dilute sulphuricacid, yields no clear film but an opaque film held together by feltedfibres. At the end of the 3 hours, the bulk of the mass is brought to0C.-

and kept at this temperature for-3 hours. There (a) 200 parts ofsoda-cellulose produced by impregnating 100 parts of sulphite cellulosewith 1000 parts of caustic soda'solution of18 per cent. strength,allowing it to stand for 6-24 hours .at' room temperature, pressinguntil the .whole weighs 200 parts, disintegr ating, and, if desired,ripening for 1-3 days, are mixed with 3 to 5 parts of carbon bisulphideand the whole is stirred or shaken or otherwise agitated for 6-12 clearand after washing I hours in a, closed, vessel at room temperature.1500to 1800'parts of caustic soda solution of g per cent. strengtharethen added, the-mass is thoroughly stirred for about -20 minutes andcooled, while stirring, to 10 to 11 C., whereby' it freezes slightly.After being kept at this temperature for about 2 to 4 minutes, theproduct is thawed. There is produced a practically colorless viscosesolutionsubstantially free from undissolved constituents, which yields afilm clear and resistant to tensile strain in the wet state, transparentand flexible in the dry state. During 14 days at room temperature nosigns of-a change are visible in the solution.

(12) 200 parts of soda-cellulose, as described in v (a), are mixed with6-7 parts by weight of carbon bisulphide and stirred or shaken for 6hours at room temperature, whereby a very slight coloration tending tolight-yellow occurs 1800 parts of caustic soda solution of 6 per cent.strength are then added and the mass is thoroughly stirred, thusproducing 'a solution, but one which contains fibres. It yields aslightly hazy film containing fibres. It is then cooled to l0" to -11 C.and kept at this temperature for half an hour, whereby it crystallizesor ature for 20 minutes to 3 hours, while a scarcely C. and kept at thistemperature for half an hour,

freezes to a mass" that can be stirred. After thawing, it is a clear,scarcely colored solution practically free' from undissolvedconstituents, which yields a transparent, flexible film. After 14 daysno indications of a change are visible in the solution. a

(c) 200 parts of soda-cellulose as in (a) are mixed with 10-20 parts byweight of carbon bisulphide and treated'therewith at roomtemperappreciable coloration occurs. 800 to 1200 parts by weight ofcaustic soda solution of 6 to 8 per cent; strength are then added; nosolution oc-' ours. The mass is then cooled to -10 -to -*1l whilestirring. After thawing, the product is a scarcely colored, fluidviscose solution, practically free from undissolved constituents, whichyields a transparent, flexible film. During 14 4 days no signs of achange are visible in the solution.

Any known process of manufacturing viscose is conducted tothe end of thesulphidizing stage,-

the sulphidized mass being then dissolved in water or caustic sodasolution at 5 C. or '10 to 11 C., according to" the foregoing examples.a

All the viscose solutions obtained by following the foregoing examples,even those produced with very small proportions of carbon bisulphide,show the characteristic metallic reactions" of viscose, for example thedistinctive red coloration with a solution of a nickel salt.

'In the following claims the expression cellulosein presence of alkaliis used not only to designate alkali cell-ulo-s'ein the usual meaning,.

that is to say the products obtainable'according to the hereinbeforeMethod 1 or 2, but also to designate mixtures of cellulose with alkalisolutionlwhich arejobtai'ned according toMethod 3.

In the rollowingj' claims 'the expression prep ,arati'onj of viscose?embraces all the proceedings from the ad'dition oficarbon bisulphide tothe production of the viscose] solution ready for use encebi 'aIkali.

The term ffreezing signifies commencing, advanced or complete separationof crystals or freezing.

I claim:

1. Process for making viscose, which process 11 comprises employing atleast temporarily temperature below 0 C., at any stage of, the processbetween the addition of the CS2 and the end of 3. Process for makingviscose, which'process 3' comprises causing the. cellulose after beingtreated with carbon bisulphide in presence of alkali to dissolve attemperatures below 0 C. i 4. Process for making viscose which processcomprises causi the cellulose. during its tr eat-' ment with carbonbisulphide in presence of alkali to dissolve at temperatures below 0 C.

5. Process for making-viscose, which process comprises treating the:cellulose with carbon bisulphide in presence of alkali for 5 minutes. to48 hours, and then subjecting it to a, tempera.- ture below 0 C., in.the presence; of an alkali 50- lution, of a, sufiicient concentrationand'ina sufficient proportion,'to dissolve the final, product.

6. Process for making viscose, which process comprises treating amixture of cellulose and an aqueous alkali solution with, carbonbisulphide and subsequently subjecting; thewhole. to-the action oftemperatures. below 0.? C.

;'Z. Process for makingviseose, which process comprises treating amixture of cellulose'and a. caustic soda solution of not more than 15wper cent. strength with carbon bisulphide and thereafter subjecting thewhole totheactionof temperatures below 0" C, I t j 8'. Process formaking viscose, which process comprises treating cellul'ose in presenceofcaustic soda solution of 4 to; 15 per cent. strength amounting to Sto24 times the weight of the. air..- dry cellulose with carbon bisulphideand thereafter subjecting the whole to the action of temperatures below0 C.

Process for making viscose, which process comprises treating alkalicellulose. with carbon bisulphide, then 1 adding. water oraqueousalka'li solution to theproductthereby obtained and, sub-5 jectingit 'to the action of temperatures. below o C p 10. Process for makingviscose, whichprocess comprises subjecting cellulose after being treatedin the presence of alkali with a proportion of carbon bisulphide whichdoes not exceed onesixth molecular proportion of carbon bisulphide toone molecularproportion of Cir-H1005 to'theaction of temperatures below0? C.

11. Processxfor making viscose, .which process comprisessubjecting-cellulose .during. its treat.- ment in presence of. alkaliwithaa proportion of, carbon bisulphide which does. not. exceed ;one-.'ixth e la pro t of ca bon. i ulphide o, ne ol c larp o i o 631006. 1 151 ct n. 0 e a ures e w. r

12. Process for making viscose, which process; comp? Em l ng PRQ X fll ha d t t e b n-b s fiqe t mp s w t sbew 9 hw s of e Pre arati n? r154.cose, and}. prolonging the cooling; treatment to, free'z'ing'l. "A w V ph 13'. Process for. makingyiscose which process comprises preparing theviscose frornlmercerized.

Ill

cellulose made by treating cellulose with alkali solution and washingwith water and employing at least temporarily temperatures below 0 C.during some stage of the operations, after the addition of CS2.

14. Process for making viscose, which process comprises preparing theviscose from cellulose which has been ground in presence of water andemploying at least temporarily temperatures below 0 C. after theaddition of the carbon bisulphide.

15. As a new product, a viscose which in its fresh crude state containsmore than ten molecular proportions of cellulose CsHmOs per onemolecular proportion of CS2.

16. As a new product, a viscose which in its fresh crude state containsmore than ten molecular proportions of cellulose CEH1005 per onemolecular proportion of CS2.

17. As a new product, a viscose which in its fresh crude state containsnot less than seven and not more than forty molecular proportions ofcellulose CeHloOs per one molecular proportion CS2, and which shows redcoloration with a solution of a nickel salt.

18. The herein described process which com prises (a) treating cellulosewith a caustic alkali solution (b) treating with carbon bisulfide and(c) dissolving the product, the temperature at some stage after thebeginning of the second step being below 0 C.

19. The herein described process which comprises (a) treating cellulosewith a caustic alkali solution (b) treating with carbon bisulfide and(c) dissolving the product, the temperature at some stage after thebeginning of the second step being low enough to convert the reactionmixture into a mass of soft lard-like consistency.

20. A process of making viscose solution which comprises mixing acellulosic material, caustic alkali, water and carbon bisulfide, in suchproportions as to convert substantially all the cellulose into viscose,and subjecting the product to a temperature below 0 C., whereby solutionof the viscose is effected.

21. A process of making viscose solution which comprises mixing acellulosic material, caustic alkali, water and carbon bisulfide, in suchproportions as to convert substantially all the cellulose into viscose,the carbon bisulfide being used in amount not substantially over 5% ofthe amount of the cellulose, and subjecting the product to a temperaturebelow O C., whereby solution of the viscose is effected.

22. A process of making viscose solution which comprises mixing acellulosic material, caustic alkali, water and carbon bisulfide, in suchproportions as to convert substantially all the cellulose into viscose,the carbon bisulfide being used in amount not substantially over 4% ofthe amount of the cellulose, and subjecting the product to a temperaturebelow 0 C., whereby solution of the viscose is effected.

23. The process for preparing viscose from cellulose, which comprisestreating the cellulose with a caustic alkali solution containing enoughcaustic alkali to form alkali cellulose, washing the alkali cellulose bya washing operation including a water wash, treating the washedcellulose with caustic alkali solution, and converting the product intoviscose.

24. The process of preparing viscose from cellulose which comprisestreating the cellulose with a caustic alkali solution containing notless than 18% of caustic alkali (calculated as NaOH) subjecting thetreated cellulosic product to a washing treatment including a waterwash, treating the washed cellulose with a caustic alkali solution andconverting the cellulosic product into viscose.

25. The process of improving bleached sulphite cellulose consisting inimmersing 100 parts of the air-dried sulphite cellulose in several timesits weight of soda lye of a concentration adapted to form sodacellulose, for at least several hours, removing the excess soda lyeuntil the material weighs 200 to 300 parts, disintegrating the pressedmaterial, and allowing to stand for about 1 to 3 days at roomtemperature, and Washing and acidifying and further washing.

26. The process of treating cellulose which comprises mixing thecellulose with several times its weight of a caustic alkali solution ofa strength adapted to form alkali cellulose, allowing the mixture tostand for several hours, pressing out the excess of the alkali solutionto leave a wet mass, comminuting the wet mass and allowing it to standfor several days, and thereafter washing out the alkali, whereby thetreated cellulose is improved.

27. The process of preparing viscose from cellulose which comprisestreating the cellulose with a caustic alkali solution containing notless than 18% of caustic alkali (calculated as NaOH) subjecting thetreated cellulosic product to a washing treatment including a waterwash, treating the washed cellulose with a caustic alkali solution andconverting the cellulosic product into cellulose xanthate, andthereafter dissolving the xanthate while at a temperature of below 0 C.

LEON LILIENFELD.

